The instant invention relates to gate valves and more particularly to such valves which include annular seats.
A conventional gate valve includes a valve body having a cavity formed therein. An inlet formed in the valve body provides fluid communication between the cavity and the exterior of the body. An outlet, typically being in axial alignment with the inlet, is formed in the body and provides fluid communication between the cavity and the exterior of the valve body. A gate, such usually being formed from one or more pieces of metal, is mounted on the valve body for lowering into the cavity for selectively shutting off fluid flow between the inlet and the outlet.
An annular metal seat ring is typically mounted on the valve body about the circumference of both the inlet and the outlet at their respective intersections with the cavity. A counterbore is provided about the circumference of the inlet and the outlet into which the seats are pressed. Each seat presents a surface toward the cavity against which the metal gate abuts in order to form a seal. The interior diameter of the seat is generally equal to the diameters of both the inlet and the outlet. An annular seal is mounted on the front surface of each seat for engaging the surface of the gate when the gate is positioned for sealing against the seats. The gate may be of the so-called expanding gate type in which the gate is formed of two or more metal pieces and includes side surfaces which are presented toward each of the annular seats. The gate also includes an opening so that when the gate is properly positioned, the opening registers with the annular seats to permit fluid flow between the inlet and the outlet. When the opening is moved downwardly out of registration with the annular seats, the gate expands to effect sealing between the gate sides and the seals on the annular seats thus shutting off the flow between the inlet and the outlet.
Such past gate valves have proved deficient in several respects. When such a valve is used to control the flow of fluids under high pressure, e.g., greater than 5,000 pounds per square inch, the seat mounted about the circumference of the inlet tends to move outwardly or blow out of the counterbore in which it is mounted when the gate is in position for shutting off fluid flow. Since it is difficult to obtain a metal-to-metal seal between the rear of the inlet seat and the bottom of the counterbore into which it is mounted, pressurized fluid may enter the space between the seat and the bottom of the counterbore thus tending to push the seat outwardly into the side of the gate. When such occurs, tremendous amounts of wear on both the seat and its annular seal occur when the valve gate is moved vertically.
When the gate is positioned for shutting off flow, high pressure fluid is pressing the gate against the outlet seat thus causing wear of the outlet seat, its annular seal, as well as the side of the gate sealed against the outlet seat.
When the seats are pressed tightly against the gate sides as described above, the seals tend to tear away or blow out from the seat surfaces when the gate is moved from a position shutting off flow to a position permitting flow. When the opening in the gate first passes across one side of the seal on, e.g., the outlet seat, fluid pressure in the opening is applied to the radially outer edge of the annular seal, whereas the radially inner edge of the annular seal is at the pressure of the outlet which is usually zero pounds per square inch. This pressure differential applied across one segment of the seal tends to force it up from the seat surface on which it is mounted, thus destroying the ability of the valve to seal off the inlet from the outlet.
In an effort to prevent the inlet seat from being blown out of the counterbore in which it is mounted, some designs have used an interference fit between the seat and its counterbore. Such construction requires a press capable of delivering many tons of force for securedly fitting the seat into the counterbore. While this may prevent blowing out of the inlet seat, it also prevents replacement of the seat unless such a press is available for applying the necessary force. In other words, if the valve is installed at a remote location, it must be removed and shipped to a point at which such a press is available for replacement of the seat.
In the case where a valve is required for use with high fluid pressures, some designs have utilized seats for both the inlet and the outlet which do not include seals. These seats are designed for providing a metal-to-metal seal against the gate on both the inlet and outlet sides. Such an arrangement is usable under high pressures; however, since high fluid pressure is required to urge the gate against the outlet seat to effect sealing, such seat designs are unworkable at lower pressures, e.g., 70 pounds per square inch. Accordingly, it may be necessary to utilize a valve of the type having annular seals mounted on the inlet and outlet seats in a low pressure situation and to use a valve of the type for effecting metal-to-metal seals in a high pressure situation. This may necessitate switching valves in an existing installation to facilitate handling of different fluid pressures.
It is a general object of the instant invention to provide a gate valve which overcomes the above-enumerated disadvantages inherent in prior art gate valves.
It is a more specific object of the invention to provide such a valve having seats which may be replaced without the use of many tons of force.
It is another specific object of the invention to provide a gate valve in which the incidence of seal blowouts is greatly reduced.
It is yet another specific object of the invention to provide a gate valve in which the wear on the seats, seals and gates is greatly reduced.
It is yet a further specific object of the invention to provide such a gate valve which may be used to seal its inlet from its outlet in the presence of fluids varying from low to high pressure.
The instant invention includes a valve body having a cavity formed therein with an opposing inlet and outlet in axial alignment, each providing communication between the cavity and the exterior of the valve body. An annular seat is received within a counterbore formed about the circumference of the inlet at its intersection with the cavity. The seat includes a rear surface, such being in sealing engagement with the valve body, and a front seat surface, such having an annular seal mounted thereon. A recess is formed on the seat surface radially inwardly from the annular seal and is in fluid communication with the inlet. An expandable gate is mounted for selected vertical positioning in the cavity for permitting fluid flow in one vertical position and for shutting off such flow by sealing against the seat surface in another vertical position.
These and other objects and advantages of the instant invention will become more fully apparent as the following detailed description is read in view of the accompanying drawings.